The assembly of the windshield, rear window and other glass elements of a vehicle to their associated body flanges is an important operation in the manufacture of vehicles, particularly from a safety standpoint. The federal government requires vehicles to pass a windshield retention test, and the materials which are used to assemble the windshield to the body flanges of the vehicle must be properly applied to pass the test and avoid expensive recalls.
The preparation of the windshield and associated body flange of a vehicle for assembly involves a number of operations. With respect to the windshield, glass manufactures supply automobile windshields with a "blackened area", i.e., an area of predetermined width along the marginal edge of the windshield which is covered with a black, ceramic frit having a roughened surface. It is the responsibility of the automotive manufacturer to prepare this blackened area for assembly to the body flange of the vehicle. First, a clear glass primer material is applied to the blackened area, usually with a wet brush manipulated by a robot or other automated brush mover. The primer may be applied to the bristles of the brush by dispensing the primer through the center of the brush. Preferably, a felt wick is dragged by the robot immediately behind the wet brush to wipe dry the clear glass primer, and to force the clear glass primer into the roughened surface of the blackened area. The clear glass primer prepares the blackened area for receipt of a coat of black glass primer material.
The next step in the preparation of the windshield for assembly to the vehicle body flang involves the application of a black glass primer over the area which had been previously coated with the clear glass primer. One method of applying the black glass primer to the windshield involves a manual operation using a flow brush or the like. This method is labor-intensive, and human applicators are prone to dripping some of the black glass primer from the brush onto areas outside of the blackened, ceramic frit. Such drips onto the clear portion of the glass are unacceptable and may require rejection of the windshield for use. Alternatively, the black material may be applied similarly to that used for the clear primer.
Another method shown schematically in FIG. 1, is to provide a continuous stream or intermittent streams, drops, of primer onto the windshield which are then distributed by a trailing pad of felt. A coating tool assembly 10 has been employed which carried two dispensing guns 12, 14 and a gripper assembly 16 which carries a pad or wick of felt 18. The dispensing guns 12, 14 have been oriented at an angle A which is substantially less than 45.degree. from the vertical centerline CL of the gripper assembly 16. For example, assemblies have been used wherein the angle A has been in the range of 20.degree.-25.degree.. In this manner, the stream or drops 20 of fluid are dispensed substantially in front of the felt 18, the direction of movement of the assembly being indicated by arrow 22, were the trailing pad of felt is used to distribute and wipe the excess of the material from the glass 24. One problem with this method is that splashing of the primer outside of the blackened area onto the clear portions of the window may occur. Another problem is that with a continuous stream of fluid, it is difficult to control the exact amount of fluid applied to the glass.
Furthermore, the gripper assembly 16 tightly holds the felt 18 in contact with the glass 24. At times, the pressure of holding the felt in contact with the glass has actually shattered the glass. Also, it has been found that the amount of film build up of either the clear or black primer on the glass is related to the pressure exerted by the felt onto the glass. If too much pressure is applied, the felt, instead of uniformly spreading the primer over the area to be covered actually may wipe away the material. In such cases, the felt may act as a snow plow, pushing the material before it to the side. This may result in a heavier build up at the outer edges with a corresponding lesser amount in the central region.
One problem which has been experienced with the application of the primers onto the blackened area of the windshield is that it is difficult to maintain the proper amount of film build up, let alone the fact that it is difficult to determine how much clear glass primer has been applied (because it is not readily visible) and whether the desired amount of the surface area of the ceramic frit has been covered. An inadequate amount or film build of clear glass primer, and/or an incomplete covering of the surface area having the ceramic frit, can result in a failure of the windshield retention test after the windshield is installed.
Another means of applying the black glass primer onto the marginal edge of the windshield is disclosed, for example, in U.S. Pat. No. 4,857,367 to Thorn et al. This patent discloses an apparatus which comprises a liquid spray nozzle, an air nozzle and a vacuum device which are movable as a unit upon a robot arm relative to the marginal edge of a windshield. The liquid nozzle sprays atomized black glass primer material in a triangular pattern onto the edge of the windshield. In order to prevent oversprayed, atomized black glass primer from being deposited onto the clear portion of the windshield, the air nozzle directs a stream of air from the interior of the windshield outwardly so as to force any oversprayed primer particles away from the interior or clear portion of the windshield. The vacuum device is located beneath and alongside the peripheral edge of the windshield to draw a vacuum and collect the oversprayed primer particles which do not adhere to the glass.
While systems of the type disclosed in U.S. Pat. No. 4,857,367 are intended to avoid the drippage problem obtained with manual application of the black primer, it has been found that the application of at least some black glass primer onto the clear portion of the windshield can still occur. The vacuum device is not completely effective in collecting the oversprayed, atomized black glass primer discharged from the liquid nozzle, and some of this oversprayed black glass primer can fall onto the clear portion of the windshield.
The function of the black primer is to bond to the clear glass primer and to provide a good bonding site to beads of adhesive or sealants, such as illustrated in EPO 379 908 assigned to Essex Specialty Products, Inc. in the assembly of automobile windshields. The black primer also acts as a blocking agent for blocking the transmission of ultra violet light to the beads of adhesive or sealant. The ceramic frit does not completely block the transmission of ultra violet light. Therefore, improper application of the black primer may result in improper bonding of the adhesive/sealant and/or the degradation of the seal due to the ultra violet light.
As a result, it is very important to be sure that enough of the primers, either clear or black, are being deposited onto the glass. If for some reason the flow of material is reduced or stopped altogether, such as due to a partial or complete blockage of flow, improper bonding of the glass to the automobile may result.